Analytical electroplating apparatus



Feb. 11, 1964 R. O. HULL, JR., ETAL ANALYTICAL ELECTROPLATING APPARATUS2 Sheets-Sheet 1 Filed April 13, 1961 INVENTOR RICHARD 0. HULL/Z BY /'CMM I f ATTORN J S Feb. 11, 1964 R. o. HULL, JR., ETAL 3,121,053

ANALYTICAL ELECTROPLATING APPARATUS ATTORNEYS BY /M,

United States Patent 3,121,053 ANALYTECAL ELECTRUPLATENG AIPARATUS Ricard 0. Hull, .l'r., Bay Village, and .loseph A. Zehnder,

Rocky River, Ulric, assignors to R. 0. Hull 8: Company, Inc., Cleveland,Ghio, a corporation of Ohio Filed Apr. 13, 1961, Ser. No. 102,818 2(Ila'nns. (ill. 204195) This invention relates to analyticalelectroplating apparatus. More particularly, it concerns electroplatingcells of a new and improved design for use in the examination andevaluation of processes of electrodeposition, electrode materials andelectrolyte compositions.

Some years ago, a new form of apparatus for the study of electroplatingwas developed which subsequently has come into widespread use as ananalytical tool. This basic type of apparatus is referred to as at Hullcell, after the original inventor, and is described in US. Patent2,149,- 344.

Although the Hull cell in general provides a very useful analyticaldevice for investigating electroplating operations, experience in theuse of such cells has revealed certain deficiencies. For example, withthe apparatus disclosed in US. 2,149,344, there is inadequate provisionfor the control of solution composition, polarization, electrolytetemperature and other variables which occur during the electrolysis.Obviously, if the results of any particular run in at Hull cell are tobe properly interpreted by the investigator, the analytical apparatusshould allow the different process variables to be controlled in a knownmanner.

One example of a difllculty which is encountered in the operation ofHull cells is variation in solution or electrolyte composition. Thus,when repeated tests are performed on a single sample of electrolyte,using the methods and apparatus available heretofore, a variation inmetal content takes place due to limitation in the size of the anodearea which is available for use. When an anode of insufficient size isused, excessive polarization also results. These factors criticallyinfluence the reliability of results and data obtained in the operationof a Hull cell, and it has been found that the ratio of the relativeanode to cathode area is of major importance in maintaining the metalcontent of the bath at a desired level.

Another difiiculty encountered in operation of Hull cells availableheretofore is the temperature rise which occurs as the electrolytesample is electrolyzed due to the passage of a relatively large currentthrough a relatively small volume of electrolyte. Since theelectroplating cells are made of material which is generally thermallynon-conductive, it has not been practical to alleviate this temperaturerise problem by surrounding the electroplating cell with a temperaturecontrolled bath.

Another problem has been variation in composition of the electrolyteduring electrolysis. This not only results in critical changes in metalcontent, but also produces changes in pH. Since pH control can be verysignificant in the type of analytical procedure which is carried out ina Hull cell, for example, in nickel plating, it is important that the pHof the electroplating solution undergo as small a change as possibleduring the analytical procedure.

Another problem encountered in the use of Hull cells is that ofmaintaining the electrolyte at controlled elevated temperatures so as toduplicate as closely as possible the conditions which will be found incommercial use of the electrolyte composition andother materialsundergoing analysis. One solution to this problem of providing elevatedtemperatures involves the placement of a heating element within adepression in the base of a Hull cell in such fashion as to reduce anyinterference in the flow of current from the anode to the cathode by theheating element (see US. 2,760,928). However, while this type of cellconstruction provides satisfactory results in the heating of theelectrolyte, it introduces new problems. Thus, additions of solidchemicals to the plating bath during an analytical operation becomeentrapped in the depression in the cell. This creates dilliculties inthe cleaning of the cell and also in maintaining proper control on theelectrolyte composition during the electroplating procedure.

A principal object of this invention is the provision of newimprovements in analytical electroplating cells of the so-called Hulltype.

Further objects include:

(1) The provision of new and improved forms of Hull cells whicheliminate or substantially reduce variations in electrolyte compositionduring use of the test apparatus.

(2) The provision or" new improvements in Hull cells which enable theanode area to be varied according to the requirements of the electrolytebeing tested, i.e., which eliminate the need for restriction of theanode to a fixed area as in Hull cells known heretofore.

(3) The provision of new improvements in such electroplating cells whichminimize pH change during electrolysis.

(4) The provision of improved analytical electroplating apparatus whichmakes possible close control of the anode to cathode ratio duringelectrolysis, resulting in satisfactory control over the metal contentof the electroplating solution.

(5) The provision of improvements in the design of Hull cells which makeit possible to include heating elements and heat control means withinthe cell without the need to form depressions or other offsets in thecell, so that such cells are easy to clean and maintain and can bemanufactured and sold at a minimum cost.

Other objects and further scope of applicability of the presentinvention will become apparent from the detailed description givenhereinafter; it should be understood, however, that the detaileddescription, while indicating preferred embodiments of the invention, isgiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this de tailed description.

These objects are accomplished according to the present invention byproviding in an analytical electroplating cell of the Hull type, apartition which extends outwardly from the side of the cell upon whichthe cathode is supported, forming a cell portion or chamber extendingoutwardly from the cathode, and then providing a second cell portion orchamber externally of this first portion and placing in the secondportion the anode elements and other auxiliary equipment which isdesired for use with the electroplating cell.

The success of the present invention is due to a large extent to thediscovery that the total volume of electrolyte contained in theelectroplating cell can be varied considerably and can be substantiallyincreased over the volume of electrolyte usable in comparable types ofcells known heretofore, so lon as the length of the cell portion orchamber formed by the partition which extends outwardly from the side ofthe cell upon which the cathode is supported is approximately equal toor greater than the width of this portion of the cell. Moreover, it hasbeen discovered that such an arrangement creates a current distributionalong the cathode panel, of such nature that reproducibility of testresults can be obtained regardless of the anode position in the portionof the cell outside of this cathode containing chamber. In addition, ithas been found that heating elements, thermostat control elements andthe like can be placed right in the cell proper without materiallyailecting the reproducibility of test results, provided these addedelements are positioned beyond the special sized cell portion or 'ice achamber facing the cathode panel. These discoveries make it possible toproduce new forms of Hull cells which alleviate the operational problemsreferred to above and also at a minimum cost, since the need for millingor special forming of the base or other portions of the cells iseliminated.

A more complete understanding of the construction of the new, improvedelectroplating cells of this invention can be had by reference to theaccompanying drawings in which:

FIG. '1 is a perspective view of an analytical electroplating cell fordetermining plating characteristics of a plating bath in accordance withthe present invention;

FIG. 2 is a plan view of the device shown in FIG. 1;

FIG. 3 is a side elevational view in partial section of the apparatusshown in FIG. 1;

FIG. 4 is a front elevation sectional view taken along the line 4 4 ofPEG. 3;

FIG. 5 is a fragmentary sectional view taken along the line 5-5 ofFIGURE 2 and enlarged with respect thereto.

Referring in detail to the drawings, the new cells of this inventionhave a cathode containing portion A and an anode containing portion B,so arranged relative to one another that a cathode member ofpredetermined cross-sectional area may be vertically mounted within theportion A and angularl-y disposed to the planes of current flow from theanode as directed by the configuration of the cell portion A.

Referring to FIG. 1 of the drawing, the new electroplating cellcomprises a base 11 to which are vertically fixed a back wall 12, a sidewall 13, a partition 14 and a front wall 15. The base and walls of thecell 19 may be made from any suitable electrically non-conductivematerial and may be joined together in any suitable fashion so as toform a fluid-tight junction along the various mating edges of the sidesand base to create a fluidtight triangular cell. Various suitablenonconductive synthetic resins are available from which the base andsides of the cell can be formed. The cells may be produced by moldingthe plastic material into the desired shape or by cementing togethersections of plastic cut out from sheet stock. Polymethacrylate has beenfound to be a particularly useful plastic from which the new cells maybe constructed.

The anode member 19 is vertically mounted against the back wall 12 suchas by being clamped thereto with the alligator clamp P which iselectrically connected to the positive side of direct current electricalsource (not shown). Similarly, the cathode member Zil is verticallymounted against the side wall 13 within the chamber A, such as by beingclamped against the wall with the alligator clamp N, which iselectrically connected to the negative pole of the direct currentsource.

A heating element 21 extends through a suitable opening 16 in the frontWall and an O-ring 2.3 is forced by the packing nut around the heatingelement 2.1 and against the outside surface of the front wall 15' toform a fluid tight junction between the opening 1e and the heatingelement 21.

A thermostat probe 22 extends into the cell through the opening 17 inthe front wall 15 and an O-ring 2 is compressed around the element 22and in contact with front wall 15 to form a liquid tight seal by thethreaded packing nut 2%, which is carried in front of the thermostatcontrol member 27. A block 28 is fixed to the outside of front wall 15to provide suitable threaded support for the packing nuts 25 and 26.

The O-rings 23 and 24 used for sealing the opening around the elements21 and 22 may be made of any suitable material which is impervious tothe action of plating solutions to be analyzed in the cell, e.g.,polychloroprene or equivalent synthetic rubber-like material.

The vertical partition 14 extends inwardly from the side wall 13approximately parallel to the front wall 15 and terminates within thecell in a vertical edge 18 short of the back wall 12. The length of thepartition 14 measured along the vertical wall 14a which faces the frontwall 15 from the junction 29 of the partition 14- with the side wall 13,to the vertical edge 18 is at least equal to the perpendicular distancebetween the opposing faces 14a and 15a of the partition 14 and the frontwall 15. Thus, the cathode chamber A which has been referred to before,is defined by the partition 14, the side Wall 13, the front wall 15, thebase 11 and a plane X-X which passes through the vertical edge 18 of thepartition 14 perpendicular to the front Wall 15. The cell portion orchamber B then comprises the remainder of the fluid containing volume ofthe cell and it is in this latter portion of the cell Where the elements21 and 22 and the anode member 19 are located.

In addition to the anode member 19, anode members 1% and 1% (asillustrated by dotted lines in drawing FIG. 2) may be employed in thecell or a single anode may be located in any one of these positionswithin the cell portion B.

Varying quantities of electrolyte may be analyzed or experimented uponby varying the depth of electrolyte introduced into the cell. Also, thesize of the anode chamber B can be substantially extended over thatillustrated in the drawings so that substantial variation in electrolytevolume can be realized using the cell constructions of this invention.The larger solution volume which can be utilized in accordance with thisinvention, with the same current density which could be employed inapparatus known heretofore, reduces the solution variation during anytest procedure. Furthermore, the unique shape of the new cells allowsvirtually unrestricted circulation of the electrolyte, thus producingmore uniform temperature conditions during electrolysis. Moreover, theability of the new cells to accommodate larger anode areas provides forimproved results in control of anode to cathode ratio and hence metalcontent of the electrolyzing solution. The increased volumes madepossible by the new cell construction also minimize pH change aselectrolysis progresses.

The new electroplating apparatus may be used in carrying out allanalytical procedures for which Hull cells are known to be useful. Thetest equipment is particularly useful in obtaining data on electrolytescontaining zinc, cadmium, copper, nickel and chromium.

A more complete understanding of the methods of use of the new apparatusmay be had by reference to the following example of actual operation inaccordance with the invention.

Example I An analytical electroplating operation is conducted usinapparatus as illustrated in the accompanying drawings, having a capacityof 534 ml. When this volume of solution is used, an addition of 4 gramsof material to the test cell corresponds to an addition of one ounceper.

gallon in a larger producing plating operation. This volume ofelectrolyte also controls the plating area on the cathode so thatestablished current density relationships are applicable. The cathodemember is 4 inches in length and 2 /2 inches in height and is immersedto a depth of 2 inches in the electrolyte, giving an immersion area of0.055 sq. ft. 7

A bright nickel electroplating solution having the following compositionis employed:

Ounces per gallon Nickel sulfate 45 Nickel chloride 7 Boric d 6 theoperation of a bright nickel solution. In prior electroplating cells ofthis general type, limitation in the size of the anode area normallyresulted in current densities higher than normal, e.g., up to 60 amp,per sq. ft.

The cell operation is observed to proceed smoothly and periodic testsduring the five minutes of operation upon the pH of the solution duringelectrolysis shows that there is a substantially less increase in pHthan is experienced in the use of prior known electroplating cells ofthis general type. Also, many more tests can be made using the sameelectrolyte without depleting the solution of important components suchas metal concentration, addition agents and brighteners.

At the completion of the run with the control solution, further runs aremade on the control solution to which additional agents, brighteners orother chemicals have been added in order to determine the elfect ofthese added materials on the electroplating results.

Example 11 A chromium plating electrolyte is tested using apparatus asshown in the accompanying drawings and described above. For this test,an electrolyte of the following composition is employed:

Ounces per gallon Chromic acid 54 Sulfuric acid 0.54

The electrolyte is heated to a temperature of 130 F. and maintainedthroughout the test procedure at this temperature by means of theautomatic thermostat control. When the electrolyte solution reaches theequilibrium temperature, the current is passed between an insolubleanode, for example, lead, having a surface area of 0.1 sq. ft. and abrass cathode with a surface area of 0.055 sq. ft. The test continuessmoothly for ten minutes at 3 amperes current and is then discontinued,the data and test results being recorded and observed as explained inUS. 2,149,- 344, which describes the basic principles and mode ofoperation of so-called Hull cells. During the ten minute test run, verylittle increase in temperature is observed in the cell, even though avery high current is employed. A constant temperature is desired becausewhen testing chromium plating electrolytes, a lower temperature mightintroduce a burn on the test cathode which would not be obtained inproduction. A higher temperature might introduce a haze which would notbe present in production. Also, since the covering power of a chromiumplating electrolyte increases as the temperature is lowered, a lowertest temperature than is used in production will produce misleadingresults by showing better covering power than is obtained in productionand conversely a higher temperature will show less covering power thanwould be obtained in production. These problems are effectivelyeliminated by the new test cell structures of this invention.

Having provided a complete description of the invention in such manneras to distinguish it from other inventions and from what is old, andhaving provided a description of the best mode contemplated of carryingout the invention, the scope of patent protection to be granted theinvention is defined by the following claims.

We claim:

1. An analytical electroplating cell comprising:

(a) a base,

(b) a vertical back wall,

(c) a vertical front wall normal to said back wall,

(d) a vertical side wall fixed at an acute angle to said back and frontwalls,

(e) said base and walls being formed of electrically non-conductivematerial and forming a fluid-tight triangular cell adopted to containplating solution to be tested,

(1) a vertical partition extending inwardly from the side wallapproximately parallel to said front wall, said partition terminatingwithin said cell in a vertical edge short of said back wall, the lengthof said partition facing said front wall from the junction of thepartition with said side wall to said vertical edge being at least equalto the perpendicular distance between the opposed faces of saidpartition and said front wall,

(g) an anode electrode vertically held against said back wall, and

(h) a cathode electrode vertically held against said side wall betweensaid partition and said front wall.

2. An analytical electroplating cell comprising:

(a) a base,

(b) a vertical back wall,

(c) a vertical front wall normal to said back wall,

(d) a vertical side wall fixed at an acute angle to said back and frontwalls,

(e) said base and walls being formed of electrically non-conductivematerial and forming a fluid-tight triangular cell adopted to containplating solution to be tested,

(f) a vertical partition extending inwardly from the side wallapproximately parallel to said front wall, said partition terminatingwithin said cell in a vertical edge short of said back wall, the lengthof said partition facing said front wall from the junction of thepartition with said side wall to said vertical edge being at least equalto the perpendicular distance between the opposed faces of saidpartition and said front wall, said partition dividing said cell into:

(g) a first cell portion defined by:

(1) a plane which passes through said vertical edge perpendicular tosaid front wall,

(2) part of said front Wall,

(3) the part of said side wall from the junction thereof with the frontwall to the junction with said partition, and

(4) said partition, and

(h) a second cell portion which constitutes the remainder of saidtriangular cell other than said first cell portion,

(i) a heating element within said second cell portion,

(j) a thermostatic element for control of said heating element withinsaid second cell portion,

(k) an anode electrode vertically mounted against said back wall, and

(Z) a cathode plate vertically held against said side wall within saidfirst cell portion.

References Cited in the file of this patent UNITED STATES PATENTS2,149,344 Hull Mar. 7, 1939 2,760,928 Ceresa Aug. 28, 1956 2,913,375Gilmont Nov. 17, 1959

1. AN ANALYTICAL ELECTROPLATING CELL COMPRISING: (A) A BASE, (B) AVERTICAL BACK WALL, (C) A VERTICAL SIDE WALL FIXED AT AN ACUTE ANGLE TOSAID BACK AND FRONT WALLS, (E) SAID BASE AND WALLS BEING FORMED OFELECTRICALLY NON-CONDUCTIVE MATERIAL AND FORMING A FLUID-TIGHTTRIANGULAR CELL ADOPTED TO CONTAIN PLATING SOLUTION TO BE TESTED, (F) AVERTICAL PARTITION EXTENDING INWARDLY FROM THE SIDE WALL APPROXIMATELYPARALLEL TO SAID FRONT WALL, SAID PARTITION TERMINATING WITHIN SAID CELLIN A VERTICAL EDGE SHORT OF SAID BACK WALL, THE LENGTH OF SAID PARTITIONFACING SAID FRONT WALL FROM THE JUNCTION OF THE PARTITION WITH SAID SIDEWALL TO SAID VERTICAL EDGE BEING AT LEAST EQUAL TO THE PERPENDICULARDISTANCE BETWEEN THE OPPOSED FACES OFSAID PARTITION AND SAID FRONT WALL,(G) AN ANODE ELECTRODE VERTICALLY HELD AGAINST SAID BACK WALL, AND (H) ACATHODE ELECTRODE VERTICALLY HELD AGAINST SAID SIDE WALL BETWEEN SAIDPARTITION AND SAID FRONT WALL.